A combustor of a gas turbine includes a nozzle assembly having a nozzle which injects fuel into compressed air from a compressor of the gas turbine, and a transition piece which leads high-temperature gas generated by mixing fuel injected from a nozzle with the compressed air and burning the mixture, to a turbine. Although the present invention is not limited to this, as the nozzle, there is a so-called dual nozzle which injects both fuel oil and fuel gas.
The dual nozzle has a double-pipe structure, as shown in FIG. 5 of, for example, Patent Document 1 below, and includes a tubular nozzle rod and a tubular oil fuel pipe which is disposed in the nozzle rod. In the nozzle rod, a gaseous fuel flow path, through which gaseous fuel passes, is formed in a portion further on the outer periphery side than a pipe insertion space in which the oil fuel pipe is inserted. Further, the nozzle rod is fixed to a nozzle mounting base which blocks a combustor insertion opening formed in a gas turbine casing. A pipe tip portion of the oil fuel pipe is fixed to a rod tip portion of the nozzle rod. A pipe base end portion of the oil fuel pipe protrudes from a rod base end portion of the nozzle rod and the nozzle mounting base and is inserted in an oil manifold fixed to the nozzle mounting base. Oil fuel is supplied into the oil manifold and flows in the oil fuel pipe from there.
When the oil fuel is injected from the dual nozzle and burned (an oil firing operation), the oil fuel pipe is cooled by the oil fuel which flows therein. On the other hand, since the nozzle rod is exposed to the flow of the compressed air from the compressor of the gas turbine, the nozzle rod is heated by the compressed air. For this reason, although the temperatures of the oil fuel pipe and the nozzle rod are uniform at the time of stopping of the gas turbine, during the oil firing operation of the gas turbine, the temperature of the nozzle rod becomes relatively high with respect to the temperature of the oil fuel pipe. Due to this difference in temperature, a difference in thermal expansion between the oil fuel pipe and the nozzle rod occurs.
Further, when gaseous fuel is injected from the dual nozzle and burned (a gas firing operation), the oil fuel pipe is not cooled by the oil fuel. For this reason, the oil fuel pipe has a temperature close to the temperature of the nozzle rod and becomes hotter than when the oil fuel is burned. However, the temperature of the oil fuel pipe does not rise as much as the temperature of the nozzle rod directly exposed to the flow of the compressed air. Accordingly, even during the gas firing operation of the gas turbine, a difference in temperatures between the oil fuel pipe and the nozzle rod occurs, and as a result, a difference in thermal expansion between the oil fuel pipe and the nozzle rod occurs.
In this manner, since a difference in thermal expansion between the oil fuel pipe and the nozzle rod occurs, although the pipe tip portion of the oil fuel pipe is fixed to the rod tip portion of the nozzle rod, the pipe base end portion of the oil fuel pipe is inserted in the oil manifold so as to be able to relatively move with respect to the oil manifold. An O-ring is disposed between the outer periphery of the pipe base end portion of the oil fuel pipe and the inner surface of the oil manifold in order to suppress leakage of the oil fuel from between them while allowing a difference in expansion of the oil fuel pipe.
Incidentally, in the dual nozzle described above, heat in the gas turbine casing is easily transmitted to the O-ring or a rod base end portion of an oil fuel rod through the nozzle mounting base and the oil manifold. For this reason, the O-ring sometimes gets damaged due to heat being applied in a short period of time.
Therefore, in Patent Document 1, as shown in FIGS. 2 and 3 of Patent Document 1, there is proposed a technique to insert the pipe base end portion of the oil fuel pipe into the oil manifold by separating the oil manifold from the nozzle mounting base and making the amount of protrusion of the oil fuel pipe from the nozzle mounting base large. In addition, in Patent Document 1, there is also proposed a technique to provide a leaked oil recovery chamber on the pipe tip portion side of the oil fuel pipe based on the O-ring in the oil manifold in order to prevent leakage of the oil fuel due to the damage to the O-ring.